Chapter 261. REST Component

Available as of Camel version 2.14

The rest component allows to define REST endpoints (consumer) using the Rest DSL and plugin to other Camel components as the REST transport.

From Camel 2.18 onwards the rest component can also be used as a client (producer) to call REST services.

261.1. URI format

rest://method:path[:uriTemplate]?[options]

261.2. URI Options

The REST component supports 4 options which are listed below.

NameDescriptionDefaultType

componentName (common)

The Camel Rest component to use for the REST transport, such as restlet, spark-rest. If no component has been explicit configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestConsumerFactory (consumer) or org.apache.camel.spi.RestProducerFactory (producer) is registered in the registry. If either one is found, then that is being used.

 

String

apiDoc (producer)

The swagger api doc resource to use. The resource is loaded from classpath by default and must be in JSon format.

 

String

host (producer)

Host and port of HTTP service to use (override host in swagger schema)

 

String

resolveProperty Placeholders (advanced)

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

boolean

The REST endpoint is configured using URI syntax:

rest:method:path:uriTemplate

with the following path and query parameters:

261.2.1. Path Parameters (3 parameters):

NameDescriptionDefaultType

method

Required HTTP method to use.

 

String

path

Required The base path

 

String

uriTemplate

The uri template

 

String

261.2.2. Query Parameters (15 parameters):

NameDescriptionDefaultType

componentName (common)

The Camel Rest component to use for the REST transport, such as restlet, spark-rest. If no component has been explicit configured, then Camel will lookup if there is a Camel component that integrates with the Rest DSL, or if a org.apache.camel.spi.RestConsumerFactory is registered in the registry. If either one is found, then that is being used.

 

String

consumes (common)

Media type such as: 'text/xml', or 'application/json' this REST service accepts. By default we accept all kinds of types.

 

String

inType (common)

To declare the incoming POJO binding type as a FQN class name

 

String

outType (common)

To declare the outgoing POJO binding type as a FQN class name

 

String

produces (common)

Media type such as: 'text/xml', or 'application/json' this REST service returns.

 

String

routeId (common)

Name of the route this REST services creates

 

String

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN/ERROR level and ignored.

false

boolean

description (consumer)

Human description to document this REST service

 

String

exceptionHandler (consumer)

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options is not in use. By default the consumer will deal with exceptions, that will be logged at WARN/ERROR level and ignored.

 

ExceptionHandler

exchangePattern (consumer)

Sets the default exchange pattern when creating an exchange.

 

ExchangePattern

apiDoc (producer)

The swagger api doc resource to use. The resource is loaded from classpath by default and must be in JSon format.

 

String

bindingMode (producer)

Configures the binding mode for the producer. If set to anything other than 'off' the producer will try to convert the body of the incoming message from inType to the json or xml, and the response from json or xml to outType.

 

RestBindingMode

host (producer)

Host and port of HTTP service to use (override host in swagger schema)

 

String

queryParameters (producer)

Query parameters for the HTTP service to call

 

String

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

261.3. Supported rest components

The following components support rest consumer (Rest DSL):

  • camel-coap
  • camel-netty-http
  • camel-netty4-http
  • camel-jetty
  • camel-restlet
  • camel-servlet
  • camel-spark-rest
  • camel-undertow

The following components support rest producer:

  • camel-http
  • camel-http4
  • camel-netty4-http
  • camel-jetty
  • camel-restlet
  • camel-undertow

261.4. Path and uriTemplate syntax

The path and uriTemplate option is defined using a REST syntax where you define the REST context path using support for parameters. 

TIP:If no uriTemplate is configured then path option works the same way. It does not matter if you configure only path or if you configure both options. Though configuring both a path and uriTemplate is a more common practice with REST.

The following is a Camel route using a a path only

from("rest:get:hello")
  .transform().constant("Bye World");

And the following route uses a parameter which is mapped to a Camel header with the key "me".

from("rest:get:hello/{me}")
  .transform().simple("Bye ${header.me}");

The following examples have configured a base path as "hello" and then have two REST services configured using uriTemplates.

from("rest:get:hello:/{me}")
  .transform().simple("Hi ${header.me}");

from("rest:get:hello:/french/{me}")
  .transform().simple("Bonjour ${header.me}");

261.5. Rest producer examples

You can use the rest component to call REST services like any other Camel component.

For example to call a REST service on using hello/{me} you can do

from("direct:start")
  .to("rest:get:hello/{me}");

And then the dynamic value {me} is mapped to Camel message with the same name. So to call this REST service you can send an empty message body and a header as shown:

template.sendBodyAndHeader("direct:start", null, "me", "Donald Duck");

The Rest producer needs to know the hostname and port of the REST service, which you can configure using the host option as shown:

from("direct:start")
  .to("rest:get:hello/{me}?host=myserver:8080/foo");

Instead of using the host option, you can configure the host on the restConfiguration as shown:

restConfiguration().host("myserver:8080/foo");

from("direct:start")
  .to("rest:get:hello/{me}");

You can use the producerComponent to select which Camel component to use as the HTTP client, for example to use http4 you can do:

restConfiguration().host("myserver:8080/foo").producerComponent("http4");

from("direct:start")
  .to("rest:get:hello/{me}");

261.6. Rest producer binding

The REST producer supports binding using JSon or XML like the rest-dsl does.

For example to use jetty with json binding mode turned on you can configure this in the rest configuration:

restConfiguration().component("jetty").host("localhost").port(8080).bindingMode(RestBindingMode.json);

from("direct:start")
  .to("rest:post:user");

Then when calling the REST service using rest producer it will automatic bind any POJOs to json before calling the REST service:

  UserPojo user = new UserPojo();
  user.setId(123);
  user.setName("Donald Duck");

  template.sendBody("direct:start", user);

In the example above we send a POJO instance UserPojo as the message body. And because we have turned on JSon binding in the rest configuration, then the POJO will be marshalled from POJO to JSon before calling the REST service.

However if you want to also perform binding for the response message (eg what the REST service send back as response) you would need to configure the outType option to specify what is the classname of the POJO to unmarshal from JSon to POJO.

For example if the REST service returns a JSon payload that binds to com.foo.MyResponsePojo you can configure this as shown:

  restConfiguration().component("jetty").host("localhost").port(8080).bindingMode(RestBindingMode.json);

  from("direct:start")
    .to("rest:post:user?outType=com.foo.MyResponsePojo");
Important

You must configure outType option if you want POJO binding to happen for the response messages received from calling the REST service.

261.7. More examples

See Rest DSL which offers more examples and how you can use the Rest DSL to define those in a nicer RESTful way.

There is a camel-example-servlet-rest-tomcat example in the Apache Camel distribution, that demonstrates how to use the Rest DSL with SERVLET as transport that can be deployed on Apache Tomcat, or similar web containers.

261.8. See Also